The present invention relates generally to horizontal deflection circuits for use in television devices such as image pickup tubes of television cameras (television camera tubes) or television picture tubes of television receivers. More particularly, the invention relates to a horizontal deflection circuit of this kind capable of carrying out horizontal deflection of constant deflection size with good linearity of the horizontal deflection operation in spite of temperature fluctuations.
In general, a horizontal deflection circuit for use in a television camera tube or a television picture tube is adapted to obtain from a horizontal synchronizing signal a current of a saw-tooth waveform for horizontal scanning and to pass this current through a horizontal deflection coil. Particularly in a horizontal deflection circuit for use in a television camera tube, good stability of linearity of horizontal deflection and deflection size is required. Furthermore, low power consumption, small size, and other features are required.
However, since a horizontal deflection coil has an electrical resistance component, in general, when a current of saw-tooth waveform is fed into the horizontal deflection coil, this current flowing through this coil becomes a current of a saw-tooth waveform whose straight-line portions are curved because of loss due to the above mentioned resistance component.
Accordingly, there has heretofore been a horizontal deflection circuit wherein a linearity correction circuit comprising a transformer, a resistor, and a power amplifier is connected to a horizontal deflection coil. This circuit is of a circuit arrangement wherein the primary winding of the transformer and the resistor are connected to the horizontal deflection coil, and the current detected by this resistor is supplied through the power amplifier to the secondary winding of the transformer. In this horizontal deflection circuit, the curved parts of the current waveform are corrented, and an operation of relatively good linearity and stability is carried out. In addition, there is also a circuit of this character wherein a thermistor is used for this resistor, and the operation is stabilized in spite of fluctuations of the ambient temperature.
These known horizontal deflection circuits, however, have a large number of circuit components. For this reason, they cannot be miniaturized, and their production cost is also high. Furthermore, these circuits are accompanied by problems such as high power consumption and their unsuitability particularly for camera tubes of portable television cameras.
Accordingly, there has been a horizontal deflection circuit wherein, instead of a large-size linearity correction circuit comprising components such as the above mentioned transformer, power amplifier, and resistor, a linearity coil of saturable reactor type is used in an attempt to realize miniaturization. This saturable reactor type linearity coil is of a construction, in general, wherein a winding is wound around a core to one end of which is closely attached a magnet for imparting a saturable reactor characteristic. This winding is connected in series to the horizontal deflection coil. As a result of a current flowing through the winding of this linearity coil, its inductance value varies, whereby linearity correction of the deflecting current is accomplished.
In a horizontal deflection circuit provided with this saturable reactor type linearity coil, since a linearity correction current is not caused to flow, the power consumption is low. Furthermore, since the small number of components are required, the circuit can be made small and has the feature of being suitable particularly for the camera tube of a portable television camera.
However, this saturable reactor type linearity coil is accompanied by a problem, as described hereinafter, in that its DC current versus inductance characteristic fluctuates with variation in the surrounding temperature. More specifically, when the temperature rises the inductance value of the coil decreases, while when the temperature falls, the inductance value of the coil increases. For this reason, a large deflection current flows at a high temperature to cause over-scanning, and the picture on the monitor screen becomes smaller than normal. On the other hand, at a low temperature, the deflection current becomes small to cause under-scanning, and the picture becomes larger than normal. Thus, the scanning size is subjected to the effect of temperature variation of the surrounding atmosphere, whereby the stability is poor.